The present invention relates to improvements to hammer mills used in association with apparatus for comminuting or chopping material such as animal feed and in particular improvements to hammer mills for tub grinders.
Tub grinders are used for chopping or grinding animal feed crops to facilitate consumption by livestock. Tub grinders are particularly well adapted for shredding, chopping and grinding large round bales of hay. Tub grinders generally comprise a stationary floor with a cylindrical side wall which rotates relative to the floor. At least one projection extending inwardly from the side wall is adapted to engage material positioned in the tub such as a round bale of hay causing the round bale to rotate with the cylindrical side wall relative to the floor. A hammer mill is generally secured below the floor of the tub grinder such that hammers and possibly one cutting blade of the hammer mill extend above the floor and into contact with the hay bale during a portion of their path of rotation. The hammers and the cutting blade cut hay from the bale and pull it into the mill where it is further ground and chopped and then ejected generally to the side of the tub grinder. A tub grinder of the type discussed is disclosed in U.S. Pat. No. 4,106,706 to Burrows.
The hammer mills in tub grinders of the type shown in U.S. Pat. No. 4,106,706 are typically oriented such that the plane of rotation of the hammers is perpendicular to the front end of the tub grinder to facilitate coupling of the hammer mill shaft to the power take off unit of a tractor used to pull the tub grinder. The mills are then designed to blow or direct hay to the side of the tub grinder.
It is advantageous in many situations to use conveyor systems in combination with tub grinders to carry the ground and chopped material further away from the grinder than it can be blown or to facilitate transfer of the material into a separate container or vessel such as a truck. Although it would be preferable to integrate such a conveyor system into the tub grinder, width considerations to permit over the road transport make it impractical to do so with side discharge hammer mills.
Further, the hammer mills in tub grinders as noted above are often ineffective when the hay to be ground or chopped is damp or wet. The damp or wet hay tends to collect on or against the internal shear plates in the hammer mill and against hammer mill side walls reducing the overall efficacy of the hammer mill and causing the hammer mill to clog up which can cause undo strain on the tractor power take off.
An additional problem with existing tub grinders of the type noted above is their inability to adequately process string and in particular plastic string used to hold the round bales of hay together. In existing tub grinders of this type, relatively long lengths of string are able to pass through the hammer mill unaffected, generally by passing along the sides of the mill and out the end generally without coming in contact with the hammers. The string can cause serious complications, including death, to cows or other livestock which ingest relatively long lengths of the undigestible string.
There is a need in the industry for an improved tub grinder with improved grinding and chopping abilities capable of processing wet hay and other feed materials and plastic string. There is also a need for such a grinder to which a conveyor may be integrally attached.